The field of this invention relates to detectors and more particularly to a detector for detecting a radioactive gas known as radon.
Radon is defined as a radioactive noble gas formed in the radioactive decay of radium, actinium, or thorium. Radon is found in some radioactive minerals and is known to be emitted from these minerals within the ground. The gas passes through the ground to the surface of the earth. Upon reaching the surface of the earth, radon is breatheable by human beings. As the gas decays, it gives off radioactive alpha particles that can be inhaled and lodge in the lungs where they continue to radiate. Certain localized areas within a given geographical area will produce a substantially increased level of radon while other localized areas will have a negligible level of radon.
This radon can be concentrated within a building or house. If this building or house is not adequately ventilated, this concentration of radon can become a health hazard. Some houses draw radon gas up from the ground, such as a chimney. If ventilation is not adequate, the carcinogenic radon gas can accumulate.
The U.S. Environmental Protection Agency has recently released findings which warns that radon, which is odorless and invisible, is the number one environmental health risk in the United States. The EPA has stated that one out of five homes in the United States may have radon concentrations that exceed the limits set by the EPA. That limit is four picocuries per liter of air. The EPA has estimated that living in a house with radon level at ten picocuries per liter would be like smoking a package of cigarettes every day. At that level, the additional risk of contracting lung cancer from radon exposure would range from thirty thousand to one hundred twenty thousand lung cancer deaths per million people over a lifetime. Tests have been conducted within different states within the United States. The percentage of the homes that exceeded the four picocuries level within each of the States differed dramatically. The worst State was Colorado at thirty-nine percent with Alabama being least at six percent.
While radon is present almost everywhere, its concentration in any given spot is unpredictable. Certain geological formations are known to contain considerable uranium deposits. However, even within such areas, individual homes can have low radon levels. Conversely, high concentrations of radon have been found where no significant uranium deposits have been identified. Indeed, one house may prove low in radon while its next door neighbor can have an unacceptably high radon concentration. In a home, radon measurements are usually made in the basement, since radon generally enters from the earth beneath the foundation. However, the risk is not confined to the basement since radon bearing air diffuses about the house. A home heating or ventilating system may also distribute the radon gas to the upper stories. There is usually no problem having to do with apartments or rooms above a building's second floor.
Only a test for the presence of radon can tell you how safe one's home or building is. There are available several types of radon detectors.
The best known laboratory instrument for measuring radioactivity, the Geiger counter, is sensitive mainly to beta and gamma radiation which is present everywhere from natural sources such as the sun. However, alpha particles, being much larger in size and slower in movement, are usually stopped by a glass wall which is common with the Geiger counter so it cannot be used to inform one much about the level of radon.
The most accurate devices for measuring radon are far too expensive for most householders to consider. There are laboratory instruments that typically cost several thousands of dollars apiece and demand expertise to use. For those reasons, these instruments are used mainly by research institutions for their accuracy and ability to make continuous hour-by-hour readings and have provided the yardstick against which other radon detectors are measured.
Previously, there have been two types of detectors which have been marketed to the general public and are relatively inexpensive. The first type is known as an alpha-track device which consists of a small sheet of polycarbonate plastic similar to a lens from a pair of sunglasses. Alpha particles that strike the plastic cause microscopic pockmarks, beta and gamma rays just pass therethrough. After exposure, typically one month to one year, the detector is to be placed within an envelope and mailed to a lab. A count of the pockmarks gives a direct measure of the mean radon concentration that the slide was exposed to within the given period of time. These type of detectors are good for long term measurement, but are ill suited for a quick test.
Other types of devices utilize activated charcoal. These activated charcoal devices function to trap radon gas. After a period of exposure, the activated charcoal container is to be shipped to a lab for analysis.
The disadvantage to both of these systems is that there is no instantaneous warning to the consumer. The radiation level within a given home or building can rise to a dangerous level and not become known to the consumer until a much later date pending the return of a lab test result. The consumer may not send the exposed medium to the lab for months after the dangerous condition arises. Plus, it is common for the lab to take a month to return the results to the consumer. During this dangerous period of time no action has been taken by the consumer. There is a need for the radon gas to be continuously monitored and if the level of radon exceeds a certain level then an immediate warning is transmitted to the consumer so immediate action can be taken.
The best form of immediate action is ventilation. Natural, fan forced, or heat recovery ventilation can get rid of as much as ninety percent of the radon in a home.